Cause right now, I’m up in here stuntin'

from Macklemore and Ryan Lewis (Ft. Macklemore & Wanz) – Thrift Shop Lyrics on Rap Genius

Meaning

Stuntin'-slang for flashy, being fly, ballin' (made famous by Big Tymers back in the day)
Showing how boss he can look in old style clothes

Macklemore is a #1 Stunna

Listen to the way Mack pronounces “here” he says it in a similar fashion to Nelly, “herre,” which can also mean “her” ie. he’s gettin' lucky with a lady due to his smoooothe moves. Possible allusion to a different type of up shirt

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